Previous studies implicate members of the Hedgehog (Hh) and Nodal signaling pathways in specification of the anterior central nervous system (CNS). The proposed studies are based on a specific hypothesis that postulates that Nodal and Hh signaling systems interact in a network. Experiments will test this hypothesis by analyzing loss and gain of function of components in both the Nodal and Hh pathways and by identifying the regulators of these pathways in a forward genetics mutagenesis screen.